The Crop Doctor
The Grains Research & Development Corporation

Australia’s costly $3.5 billion per year tussle with weeds is being fought with a shrinking arsenal, as herbicide weapons are blunted by the spread of resistant weeds.

To combat the proliferation of herbicide resistance, researchers at the CSIRO and University of WA are picking through plant genomes to uncover the ‘fountain of resistance’, or the genetic genesis of herbicide tolerance.

Detoxifying enzymes called Glutathione-S-Transferases (GST) lead plant defences against toxic threats such as herbicides. GSTs are regulated by promoter elements, which respond to herbicide chemicals and increase levels of GSTs and other detoxifying enzymes to produce resistance.

Supported by growers and the Federal Government through the Grains Research and Development Corporation (GRDC), Karam Singh’s team at CSIRO is working with Arabidopsis, a small annual of the Brassicaceae family with a modest 25,000 genes, to understand the function of GSTs and their constituent elements in lending herbicide resistance to the plant.

One Arabidopsis GST gene is switched on by 2, 4-D, Paraquat, MCPA and Dicamba. After identifying one promoter element underlying this effect, Dr Singh deleted it and re-tested the gene for herbicide response, which helped identify a second underlying element.

The two known promoter elements will be mixed in various concentrations to determine if they provide higher combined resistance levels and, if so, which mix is the most effective.

In a complementary approach, the GRDC project is using high-throughput genetic screening technology to develop mutants with higher expression of GSTs.

More than 70,000 second generation mutant seeds have been screened to find the best for testing. These lines will be compared against regular Arabidopsis under herbicide applications to determine how enhanced resistance can develop.